1. Field of the Invention
This invention relates to a limited slip differential gear mechanism, and more particularly to a limited slip differential gear mechanism by which maintenance of lubricating oil in a clearance between clutch plates as well as capacity for supplying lubricating oil to the clearance between the clutch plates are increased, whereby vibration and noise due to the stickslip phenomenon caused by friction between the two surfaces of the clutch plates being in contact with each other are prevented.
2. Related Art Statement
FIG. 1A shows an example of a limited slip differential gear mechanism comprising a differential gear casing 1 which is driven by a driving pinion (not shown) through a ring gear, a pinion shaft 2 rotating together with the differential gear casing 1, a pinion gear 3 attached rotatably to the pinion shaft 2, side gears 4 spline-connected to axles 7, and pluralities of first and second clutch plates 5 and 6 positioned between the differential gear casing 1 and the side gears 4 (A lug portion 5a of each first clutch plate 5 engages with the outer circumference of the side gear 4, while a lug portion 6a of each second clutch plate 6 engages with the differential gear casing 1). Furthermore there have been proposed heretofore such clutch plates as shown, for example, in FIGS. 1B, 1C, and 1D which have spiral or radial oil grooves 8 defined on the clutch plates wherein a differential gear carrier (not shown) is provided outside the differential gear casing 1 to maintain the entire limited slip differential gear mechanism in an enveloping state. Lubricating oil is enclosed in the differential gear carrier, and the interior and exterior of the limited slip differential gear mechanism are communicated with each other through openings, clearances or the like defined in the differential gear casing 1 so that the lubricating oil passes freely to and from the limited slip differential gear mechanism.
In the above construction, when the torque introduced from the drive pinion (not shown) through the ring gear is transmitted to the differential gear casing 1, the pinion shaft 2 fitted thereto is also rotated by means of the turning force acting on the differential gear casing 1, and such turning force is transmitted to the pinion gears 3 fitted to the pinion shaft 2, the side gears 4 meshed with the pinion gears 3, and the clutch plates 5 and 6, respectively. As a result, the clutch plates 5 and 6 function as a by-pass for torque to transmit the same in a manner such that much more torque is transferred to the axles 7 on the lower speed side by an amount corresponding to the torque capacity, whereby tractive ability, running stability and the like can be improved.
In limited slip differential gear mechanisms, however, the clutch plates 5 and 6 are disposed between the side gear 4 and the differential gear casing 1, and the surface of each clutch plate is flat-finished, so that it becomes rather difficult to supply lubricating oil into a gap between the sliding surfaces, and this results easily in a shortage of a lubrication film therebetween. Thus, wear occurs at in the sliding surfaces to lower the performance and at the same time to generate the stick-slip phenomenon due to friction between the surfaces of the clutch plates 5 and 6. Thereby, there is the danger that tyres and the axle 7 resonate as a spring system, whereby vibration of the clutch plates 5 and 6 is transmitted to the differential gear casing 1 and the like by repeating accumulation and release of torque, and thus generating an abnormal sound. In this connection, there is a problem that such abnormal sound is undesirable to a passenger.
The term "stick-slip phenomenon" used herein means the phenomenon which appears due to static friction in the case of contact between two surfaces and dynamic friction in the case of sliding between two surfaces, when considered friction in face to face relation, and such stick-slip phenomenon produces vibration.
In such a limited slip differential gear mechanism wherein any clutch plate shown in FIG. 1A, 1B, or 1C is used, the lubricating oil which is introduced into the oil groove 8, upon stopping the limited slip differential gear mechanism, forms a film of oil extending on the surface of the clutch plates by means of slidable contact between the two clutch plates upon starting application of pressure to the clutch plates when action of the limited slip differential gear mechanism is commenced. But, when the action of mechanism continues continues the action thereof, neither fresh oil is not supplied to the oil groove 8, and the lubricating oil in the oil groove 8 as well as such lubricating oil which will form a film rapidly flow out and scatter by means of centrifugal force, so that there is the possibility that the above-mentioned stick-slip phenomenon appears.